Eddy current retarder

ABSTRACT

An eddy current retarder having a rotor part of the retarder with symmetry of revolution about the axis of the engine shaft so that it has a peripheral face facing a peripheral face of the stator part, the inductor of the retarder having at least one electromagnetic winding. Thus, the Eddy current retarder maintains a compact structure while at the same time allowing simple and easy control over its magnetic flux by virtue of the presence of electromagnets.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a national phase of PCT/FR00/03612 filed Dec. 20,2000, claiming priority of French Appln. No. FR 99 16241, filed Dec. 22,1999, all of which are included in their entirety by reference madehereto.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an Eddy current retarder for a vehicle,intended to slow the rotation of a shaft driven about its axis.

Among such retarders, the invention relates more especially to thosewhich are intended to slow the rotation of an engine shaft driven aboutits axis, particularly the crankshaft of a vehicle engine, this enginehaving a casing which itself comprises a frontal wall stretchingsubstantially in a plane perpendicular to the axis of the crankshaft,which crankshaft has one end which is directed toward the frontal wallof the casing of the engine and in the region of which the retarder ismounted overhangingly on the frontal wall of the casing of the enginevia connecting means, the retarder comprising a rotor part which rotatesas one coaxially with the crankshaft, a stator part coaxial with thecrankshaft and secured to the frontal wall of the casing of the engine,an armature belonging to the rotor part and an inductor belonging to thestator part, the inductor being arranged on a stationary annularcomponent of the stator part, facing the armature.

2. Description of the Prior Art

Document JP9201037 describes an Eddy current retarder of theabovementioned type.

Such a retarder has the advantage of having a simplified structure and alow weight and size, given its geometry with a ferromagnetic centraldisk rotating as one with the crankshaft and rotating between two diskswhich support energizing means consisting of permanent magnetsprojecting axially toward the central disk, it being possible also forone of the two disks with permanent magnets to be rotated by aservomotor.

However, the main disadvantage with this retarder is that its brakingtorque is difficult to control. This is because two disks are equippedwith permanent magnets, the magnetic flux of which is difficult tocontrol. In particular, this retarder does not make it possible tocompletely cancel the magnetic flux, particularly the magnetic fluxtangential to the disks, which remains very high.

Another disadvantage of this retarder lies in the fact that it isarranged between the engine and a pulley that drives the timing andaccessories, said pulley being situated at the output of the crankshaft.What this means is that the pulley, thus distanced from the engine, willgive rise to a significant overhang of the belt that drives the engineauxiliaries, which belt habitually runs around this pulley, such anoverhang entailing moving all the accessories, and therefore creating asimilar overhang in said auxiliaries in order to avoid, in the longterm, causing this belt running around the pulley to break.

BRIEF SUMMARY OF THE INVENTION

A particular object of the present invention is to overcome thesedrawbacks.

To this end, the rotor part of the retarder according to the inventionhas symmetry of revolution about the axis of the crankshaft so that ithas a peripheral face facing a peripheral face of the stator part, theinductor of the retarder having at least one electromagnetic winding.

Thus, the Eddy current retarder maintains a compact structure while atthe same time allowing simple and easy control over its magnetic flux byvirtue of the presence of electromagnets.

In some preferred embodiments of the invention, recourse is had to oneand/or other of the following arrangements:

the rotor part has an external component of substantially cylindricalshape which surrounds the stator part and which constitutes the armatureof the retarder, said external component having a radial flange securedto the crankshaft, said flange being pierced with a number of holes;

the inductor of the retarder is an inductor with poles each surroundedby an induction winding and projecting radially outward on the externalface of said annular component of the stator part;

the poles are secured to a first annulus, while the collection ofinduction windings constitutes a second annulus of larger diameter thanthat of the first annulus, said second annulus being assembled coaxiallywith said first annulus by fitting each pole into a respective inductionwinding;

the inductor of the retarder is an inductor with claws and with onesingle induction winding;

a first set of claws constitutes a first annulus and a second set ofclaws constitutes a second annulus with the same diameter as that of thefirst annulus, said induction winding surrounding a cylindricalcomponent of a diameter smaller than that of the first and secondannuli, these being assembled coaxially with said cylindrical componentin such a way that each claw of the first set of claws is interspersedbetween two adjacent claws of the second set of claws;

the connecting means comprise a framework which has at least onesubstantially radial flange centered on the crankshaft and pierced witha number of holes, said flange itself having arms which extend from ittoward the engine to secure the framework to the frontal wall of thecasing of the engine, the electromagnetic retarder being housed in aspace delimited by the flange, the fixing arms and the frontal wall ofthe engine;

a pulley situated at the output of the crankshaft is arranged betweenthe casing of the engine and the retarder; the flange of the externalcomponent advantageously incorporating the pulley, so as to reduce thenumber of parts in the assembly;

said induction winding (or windings) is (or are) energized from anelectrical source, which is regulated for power, of the vehicle.

Other features and advantages of the invention will become apparent inthe course of the following description of one of its embodiments, whichare given by way of nonlimiting example with reference to the appendeddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is an exploded perspective view of the Eddy current retarderaccording to a first embodiment of the invention, before it is mountedon the casing of the engine;

FIG. 2 is a view in cross section of the retarder of FIG. 1, after itsrotor and its stator have been assembled;

FIG. 3 is a perspective view of the retarder of FIG. 1, depicting thelatter in its position mounted on the casing of the engine;

FIG. 4 is a schematic exploded perspective view of an alternative formof the stator of the retarder of FIGS. 1 and 2.

BRIEF DESCRIPTION OF THE INVENTION

Referring to FIGS. 1 and 2, a first embodiment of the Eddy currentretarder 1 according to the present invention comprises an armaturerotor 2 which rotates with a shaft rotated about a substantiallyhorizontal axis X, this shaft consisting, in particular, of thecrankshaft cs of a vehicle engine M. This engine comprises a casing 3which itself has a frontal wall 3 a stretching substantially in a planeperpendicular to the axis X of the crankshaft cs. The Eddy currentretarder 1 further comprises an inductor stator 4 comprisingelectromagnetic windings 5 which consist respectively of coils.

The aforementioned retarder 1 is intended to be arranged at the outputof the crankshaft cs, on the same side as the pulley 6, and therefore onthe opposite side to the output of the engine shaft that is connected tothe gearbox, said retarder being mounted overhangingly on the frontalwall 3 a of the casing 3 of the engine M as depicted in FIG. 3. Unlikethe arrangement anticipated in the prior art described above, it iscontrived for the pulley 6, which conventionally lies at the output ofthe crankshaft, and which is intended to be surrounded by a belt 7suitable for driving the engine auxiliaries, such as the camshafts 8 andthe alternator 9 in particular, together with the water pump, to beinserted between the retarder 1 and the frontal wall 3 a of the casing 3of the engine M so as to eliminate any problem of aligning the belt 7with the auxiliaries it drives. This solution proves thus to be far morecompact than the one adopted in the prior art described above, becauseit does not entail compensating for the overhang of the pulley and ofthe belt by creating an overhang of the auxiliaries it drives.

More specifically, with reference to FIGS. 1 and 2, the rotor 2 has anexternal component which is substantially cylindrical of revolutionabout the axis X and which has a circular cross section. This componentis hollow so that it surrounds the stator 4. It has an envelope 10 andan end wall 11 forming a flange, the assembly being made of aferromagnetic material, generally of steel, and equipped, on the outsideof the envelope 10, with ribs 12, for example helical ribs, formedintegrally with the envelope 10 and which are intended to act asradiator fins to cool the rotor 2 heated by the Eddy currents. Theseribs 12 are also capable, if they have a suitable profile, of causingthe rotor 2 to act like a fan, sweeping a stream of cooling air over thehot surfaces of the rotor 2 that need to be cooled, when the retarder isin use. The rotor 2 is arranged coaxially with the axis X of thecrankshaft cs, the flange 11 being fixed to the crankshaft cs by meansof an axial screw which passes through the flange 11 and is fixed intothe end facing it of the crankshaft cs. The flange 11 has a peripheralrim which is pierced with a number of holes 13, for example circularones, the usefulness of which will be seen later on in the description.In addition, the flange 11 may incorporate the pulley 6, these twoelements then being produced as a single piece with the rest of thearmature rotor 2.

In the example depicted, the stator 4 comprises two annuli 14 and eachof which has a substantially annular shape. Polar cores 16 project fromthe external peripheral surface of the annular 14, in a radial directionwith respect to the latter. Said polar cores, of which there are twelvein the example depicted, but of which there may be any number, areuniformly distributed about the annulus 14, each polar core stretchingparallel to the axis X of the crankshaft cs. The annulus 15 for its partconsists of a succession of twelve electromagnetic coils 5 closetogether so that they substantially define a circle centered on the axisX of the crankshaft cs. The annulus 15 has a diameter slightly greaterthan that of the annulus 14 so that it can be assembled coaxially withthe annulus 14 by fitting each polar core 16 into a respective coil 5.

The various electromagnetic coils 5 are connected to a source of directcurrent, such as, for preference, the battery (not depicted) of thevehicle, via appropriate control and regulating devices (not depicted).

When the retarder is powered, an electric current runs through theelectromagnetic coils 5 and these generate Eddy currents in the rotor 2which thus passes in front of the polar cores 16 which are alternatelypositive and negative. This results in a torque which slows thecrankshaft cs and heats the rotor 2, which heating is partiallycompensated for by the ventilation afforded by the ribs 12.

Such a mounting of the stator 4 therefore advantageously allows themagnetic flux to be controlled in a simpler and quicker way than in theretarder described in the prior art mentioned hereinabove. It is thuspossible to completely cancel this flux by cutting off the currentdelivered by the battery.

It is contrived for the inductor stator assembly consisting of theassembly of the two annuli 14 and 15 to have a diameter and an axiallength which are slightly smaller than those of the rotor 2, so thatwhen the retarder 1 is being assembled, this assembly is introduced intothe external component of the rotor 2, a small (for example with athickness E of 1 to 3 mm) gap being left between the internal surface ofthe envelope 10 of the rotor 2 and the corresponding polar cores 16 ofthe annulus 14 of the stator 4. Such an arrangement thus makes itpossible for the external component of the rotor 2 to travel past thepolar cores 16 of the stator 4.

It should incidentally be noted that the hollow cylindrical shape of theretarder 1 according to the present invention makes it incontestablylighter and less expensive than the disk-type retarder of the prior artdescribed hereinabove.

Still with reference to FIGS. 1 and 2, the annulus 14 of the stator 4 isequipped, on its interior periphery, with bosses 17 which extend in thedirection of the axis X of the crankshaft cs. In the example depicted,there are six of these bosses and they are arranged in the continuationof a first, third, fifth, seventh, ninth and eleventh successive polarcore 16. Each of the bosses 17 is pierced with a tapped axial bore 18,intended to take a screw (not depicted) for securing the annulus 14 ofthe stator 4 to a framework 19. This framework is itself intended to besecured to the frontal wall 3 a of the casing 3 of the engine M of thevehicle, as is depicted in FIG. 3.

The framework 19 is a rigid component which can be made, for example, ofcast iron and aluminum alloy. This component comprises a flange 20 whichhas a substantially annular shape and is arranged in a more or lessradial plane coaxial with the axis X of the crankshaft cs. The flange 20has a central opening 21 to lighten it. It also comprises a peripheralpart 22 which is pierced with a number of holes 23, for examplerectangular ones, the utility of which will be seen later on in thedescription. The framework 19 also comprises arms 24 which each stretchaxially in the direction of the axis X of the crankshaft cs, from theouter edge of the peripheral part 22 of the flange 20. Each arm 24 has abase 25 pierced with a hole 26 which is designed to take a screw (notdepicted) so that the framework 19 can be secured to the frontal wall 3a of the casing 3 of the engine M, as is depicted in FIG. 3. In theexample depicted, there are three arms 24 and they are distributed atuniform spacings of 120° about the flange 20. The internal edge of theperipheral part 22 of the flange 20 is, for its part, provided withsecuring parts 27 each of which comprises a tapped hole. These securingparts 27 are six in number and are distributed at uniform intervalsaround said internal edge. They are also arranged in such a way thatwhen the retarder 1 is mounted on the framework 19, they comerespectively into register with the bosses 17 of the annulus 14 of thestator 4 so that the screws, associated respectively with the bosses 17,can be screwed into the tapped holes of the securing parts 27, thisbeing so as to secure the annulus 14 of the stator 4 to the framework19.

Furthermore, it is contrived for, on the one hand, the flange 20 to havean outside diameter slightly greater than that of the envelope 10 of therotor 2 and, on the other hand, for the securing arms 24 to have alength which is slightly greater than the axial length of the rotor 2,so that in the mounted position on the frontal wall 3 a of the casing 3of the engine M, the retarder 1 is housed entirely between the flange 20of the framework the arms 24 thereof and the frontal wall 3 a of thecasing 3 of the engine M, as can be seen in FIG. 3.

Such a configuration of the framework 19 and of the retarder 1 thusmakes it possible to produce a compact assembly of the retarder 1 on thecasing 3 of the engine M. Furthermore, the rotor 2 has the advantage,given its shape and arrangement, that it can act as a flywheel,supplementing the flywheel 28 as depicted in FIG. 3, which is arrangedagainst the rear wall 3 b of the casing 3 of the engine M.

This assembly also has the advantage of being particularly light inweight, not only because of the hollow cylindrical geometry of theassembly consisting of the framework 19 and of the retarder 1, but alsobecause of the presence of the holes 13 and 23 made respectively in theflange 11 of the rotor 2 and in the flange 20 of the framework 19. Itshould be noted that the holes 13 and 23 also have a function ofallowing cooling air to circulate in the direction of the stator 4 so asto reduce the heating of the electromagnetic coils 5. Furthermore, thecollection of holes 13 forms a thermal barrier which prevents the heatenergy dissipated by the retarder 1 from propagating by conduction inthe direction of the pulley 6.

An alternative form of the stator 4 of the retarder 1 of the inventionwill now be described with reference to FIG. 4.

In this second embodiment, the retarder 1 comprises, as in the firstembodiment described hereinabove, a rotor 2 which is in every respectidentical to the rotor depicted in FIGS. 1 and 2 and which, for thisreason, is neither described in detail nor depicted. The retarder 1 ofFIG. 4 can be distinguished from that of FIGS. 1 and 2 only in that ithas a stator 4′ made in three parts rather than two.

More specifically, this stator 4′ comprises a component 4′a which issubstantially cylindrical of revolution about the axis X and of circularcross section. The cylindrical component 4′a comprises an envelopesurrounded by a conducting wire 5′ which is wound in such a way as toform several successive turns 5′a of circular cross section. In a wayknown per se, the collection of these turns of wire 5′a constitutes theinduction winding of the retarder 1. In the same way as the variouselectromagnetic coils 5 of the first embodiment depicted in FIGS. 1 and2, the turns 5′a wound around the cylindrical component 4′a areconnected to a source of direct current such as, for preference, thebattery (not depicted) of the vehicle.

In the example depicted in FIG. 4, the stator 4′ further comprises twoannuli 14′ and 15′ each of which has a substantially annular shape.These annuli are in every respect identical and consist respectively ofa radial flange 14′a or 15′a pierced with a coaxial central hole 29 andwith a succession of claws 14′b, 15′b which, in the example depicted,have a substantially triangular shape. The claws 14′b and 15′b aredistributed at regular intervals about their respective annulus, eachclaw 14′b, 15′b stretching in the direction of an axis parallel to theaxis X of the crankshaft, from the peripheral edge of the flange 14′a,15′a associated with it. The annuli 14′ and 15′ have a diameter slightlygreater than that of the cylindrical component 4′a so as to be assembledon the latter, said annuli 14′ and 15′ then being arranged coaxiallywith the cylindrical component 4′a. The axial length of the annuli 14′and 15′ is determined in such a way that they, between them,substantially completely surround the cylindrical component 4′a, eachclaw 14′b of the annulus 14′ being interspersed between two adjacentclaws 15′b of the annulus 15′.

As mentioned previously in the context of the first embodiment of theretarder 1 depicted in FIGS. 1 and 2, it is contrived for the assemblyconsisting of the assembly of the two annuli 14′ and 15′ on thecylindrical component 4′a to have a diameter and an axial length whichare slightly smaller than those of the rotor 2, so that when theretarder is mounted, this assembly is completely introduced into theexternal component of the rotor 2, a small (for example 1 to 3 mm wide)gap being left between the internal surface of the envelope 10 of therotor 2 and the corresponding claws 14′b and 15′b of the stator 4′,which thus makes it possible for the external component of the rotor 2to travel past the claws 14′b and 15′b of the stator.

The way in which the retarder equipped with the stator 4′ works issimilar to the operation of the retarder according to the firstembodiment described hereinabove. What this means is that when theretarder according to the second embodiment is powered, an electriccurrent passes through the collection of turns 5′a and generates Eddycurrents in the rotor 2 which then travels past the claws 14′b and 15′bof the stator 4′ which are alternately positive and negative. Thisresults in a torque which slows the crankshaft cs.

In a similar way to the stator 4 as illustrated in FIG. 1, the annulus14′ of the stator 4′ is pierced with peripheral holes 18′ each of whichis intended to take a screw (not depicted) so that said annulus 14′ canbe secured to the framework 19.

What is claimed is:
 1. Eddy current electromagnetic retarder forreducing rotation of a crankshaft of a vehicle engine driven about anaxis, said engine having a casing wherein said casing comprises afrontal wall stretching substantially in a plane perpendicular to saidaxis of said crankshaft, said crankshaft shaft has one end directedtoward said frontal wall of said casing of said engine, the retarderbeing mounted overhangingly on said frontal wall of said casing of saidengine via connecting means, the retarder comprising a rotor part whichrotates coaxially with said crankshaft, a stator part coaxial with saidcrankshaft and secured to said frontal wall of said casing of saidengine, an armature operatively attached to said rotor part and aninductor operatively attached to said stator part, said inductor beingarranged on a stationary annular component of said stator part, facingsaid armature, wherein said rotor part has symmetry of revolution aboutsaid axis of said crankshaft so that said rotor part has a peripheralface facing a peripheral face of said stator part, said inductor of saidretarder having at least one electromagnetic winding.
 2. The retarder asclaimed in claim 1, wherein said rotor part has an external component ofsubstantially cylindrical shape which surrounds said stator part andwhich constitutes said armature of said retarder, said externalcomponent having a radial flange secured to said crankshaft, said flangebeing pierced with a number of holes.
 3. The retarder as claimed ineither of claims 1 and 2, wherein said inductor of said retarder is aninductor with poles each surrounded by an induction winding andprojecting radially outwardly on an external face of said annularcomponent of said stator part.
 4. The retarder as claimed in claim 3,wherein said poles are secured to a first annulus and the collection ofinduction windings constitutes a second annulus of larger diameter thanthat of said first annulus, said second annulus being assembledcoaxially with said first annulus by fitting each pole into a respectiveinduction winding.
 5. The retarder as claimed in either of claims 1 and2, wherein said inductor of said retarder is an inductor with claws andwith one single induction winding.
 6. The retarder as claimed in claim5, wherein a first set of claws constitutes a first annulus and a secondset of claws constitutes a second annulus with the same diameter as thatof the first annulus, said induction winding surrounding a cylindricalcomponent of a diameter smaller than that of the first and secondannuli, said annuli being assembled coaxially with said cylindricalcomponent in such a way that each claw of the first set of claws isinterspersed between two adjacent claws of the second set of claws. 7.The retarder as claimed in either of claims 1 and 2, wherein saidconnecting means comprise a framework which has at least onesubstantially radial flange centered on said crankshaft and pierced witha number of holes, said flange having arms extending from said flangetoward said engine to secure said framework to said frontal wall of saidcasing of said engine, the electromagnetic retarder being housed in aspace delimited by said flange, said fixing arms and said frontal wallof said engine.
 8. The retarder as claimed in either of claims 1 and 2,wherein a pulley situated at an output of said crankshaft is arrangedbetween said casing of said engine and the retarder.
 9. The retarder asclaimed in claim 1, wherein said rotor part has an external component ofsubstantially cylindrical shape surrounding said stator part andconstituting said armature of the retarder, said external componenthaving a radial flange secured to said crankshft, wherein said flangebeing pierced with a number of holes; said retarder further comprises apulley being situated at an output of said crankshaft and arrangedbetween said casing of said vehicle engine and said retarder, whereinsaid flange of said external component incorporates the pulley.
 10. Theretarder as claimed in either of claims 1 and 2, wherein said inductionwinding is energized from an electrical source, which is regulated forpower, of the vehicle.